A polyarylate resin is a polyester containing a bisphenol component and an aromatic dicarboxylic acid component as monomeric components. Because a polyarylate resin is excellent in transparency, heat resistance and mechanical strength, it is used as optical parts, protective films, electrical and electronic parts, etc. In these applications, a need for performing wet spinning, coating and spraying from a resin solution as a method of processing resin has been increasing in order to comply with a demand of weight saving and reduction in thickness of polyarylate resin products. For this reason, a polyarylate resin is required to have a dissolving property and a solution stability to an organic solvent. However, the most general polyarylate resin using 2,2-bis(4-hydroxyphenyl)propane as a bisphenol component has been problematic in that a dissolving property and a solution stability to an organic solvent are insufficient.
An attempt has been made to obtain a polyarylate resin with a dissolving property and a solution stability to an organic solvent improved by using a bisphenol in which the 3-position, or the 3-position and 5-position of a benzene ring are substituted as the bisphenol component. For example, Patent Document 1 discloses the technique of obtaining a polyarylate resin which is excellent in preservation stability of a coating liquid when a solvent such as methylene chloride is used, with the use of 2,2-bis(3-methyl-4-hydroxyphenyl)propane and a specified polymerization catalyst. Patent Document 2 discloses the technique of obtaining a polyarylate resin using a bisphenol in which the 3-position and 5-position of a benzene ring are substituted. However, the polyarylate resins obtained by these techniques have a new problem that a reactivity with the other material and adhesive properties to various materials are insufficient. If the adhesive properties of the polyarylate resin to various materials are insufficient, in both the case where the polyarylate resin is used as a film material and the case where the polyarylate resin is used as a substrate material on which a film is formed, the film is easily peeled. When a bisphenol is used in which the 3-position and 5-position of a benzene ring are substituted, there is also a problem that an ultraviolet-absorbing property manifested by photo Fries rearrangement reaction of the polyarylate resin is deteriorated. If the ultraviolet absorbing property is deteriorated, ultraviolet rays which enter an optical part formed from the polyarylate resin may permeate the polyarylate resin to degenerate the inside of the optical part or a side opposite to the irradiation surface.
On the other hand, it is known that a polyarylate resin obtained by interface polymerization includes an acid anhydride bond “—C(═O)—O—C(═O)—” generated by a dehydrochlorination reaction between an acid chloride and a carboxyl group generated by hydrolysis of the acid chloride. It has been previously known the technique of adjusting the amount of the acid anhydride bond contained in the polyarylate resin for improving compatibility with the other resin during kneading in the molten state (Patent Document 3). However, when the polyarylate resin using 2,2-bis(4-hydroxyphenyl)propane described in Patent Document 3 is dissolved in a polar organic solvent having a high hygroscopic property, such as N-methylpyrrolidone, to be used, an acid anhydride bond in the resin is hydrolyzed by moisture derived from moisture absorption, so that there is a problem of lowering a solution stability. If the solution stability of the polyarylate resin is lowered in a polar organic solvent having a high hygroscopic property, insolubles are generated in the solution due to preservation in the solution form, so that transparency and smoothness of a film obtained by using the solution are lowered.
Accordingly, in the prior art, a polyarylate resin has not yet been obtained which is excellent in all of an ultraviolet-absorbing property, a dissolving property in an organic solvent, a solution stability in a polar organic solvent having a high hygroscopic property, a reactivity with the other material and adhesive properties to various materials.